1. Field of the Art
Relatively large quantities of lubricants are used in the production of unplasticized films of emulsion PVC of high K-value, such as adhesive tape films. The lubricants are normally added in quantities of at least 4 phr (i.e., 4 parts by weight lubricant to 100 parts by weight synthetic resin) and more. Diphenyl thiourea or alkyl tin thioglycolates are generally used as stabilizers.
The choice of the lubricant is determined not only by lubricating effect and release effect of the lubricant, but most importantly by lubricant compatibility with the substrate. Only a few lubricants are compatible with rigid PVC in quantities of 4 to 5 or even 6 phr. In addition, the lubricants used with emulsion PVC also have to be compatible with the emulsifier used for polymerization and still present in the polymer.
2. Discussion of Related Art
The requirements of PVC production processes and the desired product properties are still best satisfied by lubricants based on montanic acid derivatives, such as montanic acid esters and partially hydrolyzed montan waxes. Unfortunately, the availability of montan waxes and derivatives thereof is limited and subject to certain fluctuations. For this reason alone, there is a need for lubricants to replace the montanic acid derivatives. In addition, the use of lubricants based on montanic acid derivatives is attended by the disadvantage that the formulations of the plastic molding compositions are totally inflexible in regard to the lubricant component, so that there is no possibility of influencing the lubrication behavior of the molding compositions or the color, transparency and wettability of the film by modifying the lubricant. For example, it is not possible to increase the aqueous solution wettability of rigid PVC films containing montanic acid derivatives as lubricants to the extent that aqueous primers may be used instead of the increasingly less desirable solvent-based primers presently employed.
Further, known lubricants based on montanic acid derivatives cannot readily be replaced by wax esters of analogous structure, i.e., fatty acid alcohol esters. Medium-chain wax esters are extremely compatible with rigid PVC in quantities of 1 to 2 phr; if that quantity is doubled, however, the esters become totally incompatible so that a PVC film formulation containing 4 phr cetyl palmitate, for example, is completely over-lubricated.